Conventionally, there is provided a printing system having a plurality of print servers clustered (for example, see Patent Document 1). In the printing system of this type, when a trouble is caused by one of the print servers, a backup print server takes over and executes a print job managed by the print server causing the trouble.
Referring to the print control device described in the Patent Document 1, when another print server takes over print job information of the print server which goes down, it is decided whether a status of the print job information is a takeover target. If it is decided that the status is the takeover target, the print job information decided to be the takeover target is added to a job list held by the print server.
Specifically, it is decided whether the status is the takeover target from the following three viewpoints.                If the print server goes down in a transfer state from a spool, transfer to a print device has not been carried out. For this reason, the takeover is not performed.        A job executing interruption after the transfer has already been transmitted to the print device and there is a possibility that discharge of a paper might have been started. For this reason, job tracking is taken over to confirm completion, thereby preventing double printing.        If the print job has already been completed or ended due to an error, the status is not set to be the takeover target.        
There is also provided a printing system which clusters a plurality of printers and performs proxy printing by another printer when a failure occurs in a printer which is being used (for example, see Patent Documents 2 and 3). Referring to the network managing device described in the Patent Document 2, when a failure occurs in a printer which is executing print processing based on an input print job, a proxy print job configured from print data which was not printed by the printer causing the failure and a control code of the print data is created based on failure occurrence information from which a notice is given from the printer to a print server, and the proxy print job thus created is output to a proxy printer.
Referring to the distribution processing system for a print job described in the Patent Document 3, moreover, when an error occurs in a partner printer, continuation of printing is stopped until the error is eliminated by one of printers making a pair. Then, a noted distribution destination printer receives unprinted page information from a printer controller, and furthermore, receives a distribution job stored in a printer buffer, changes control data on the distribution job, and generates an unexecuted job requiring for printing an unprinted page and supplies the unexecuted job to the partner printer.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2009-151470
Patent Document 2: Japanese Laid-Open Patent Publication No. 1997-231025
Patent Document 3: Japanese Laid-Open Patent Publication No. 2007-62059
In the case in which a plurality of print servers or a plurality of printers is clustered to build a printing system, continuous execution is demanded without stopping the printing when a failure occurs in any of the print servers or printers. In the case in which a failure occurs during execution of a print job for a plurality of pages so that another print server or printer takes over the print job, moreover, it is also demanded to prevent double print of the same page from being caused by performing the print job again from the beginning.
In contrast, according to the system described in the Patent Document 1, there is provided a function for preventing double printing when another print server takes over a print job of a print server which goes down. However, this function serves to prevent the double printing by taking over tracking of the print job to confirm completion in the case in which the print job has already been transmitted to a print device. On the other hand, the takeover is not performed when the print server goes down in a transfer state from a spool. For this reason, there is a problem in that the print might be stopped.
Also in the systems described in the Patent Documents 2 and 3, furthermore, when a failure occurs in a printer which is performing print, a print job for giving an instruction for printing an unprinted page is generated to carry out proxy print by another printer so that the same page can be prevented from being subjected to double printing. However, the systems described in the Patent Documents 2 and 3 need to generate a print job for an unprinted page when performing the takeover. For this reason, there is a problem in that the print is stopped temporarily. By exactly taking over an original print job by another printer, it is possible to shorten a stoppage time for the print. However, the double printing cannot be avoided.